Your lower blue line is a conning officer's platform, also used by the leadsman. The upper blue line should be continued left to end above the end of the lower blue line. This is the safety line over the platform. You can see several vertical stanchions between the two blue lines. This platform was needed to give the conning officer a better view of what was ahead in close maneuvering. You can see such platforms on many of the big merchant liners (like Titanic).
Thanks, I'd totally buy that analysis for a dollar.
If I could justify carving out from my copious spare time, I've been thinking that this would make a great model (in the same scale as the Lindberg 'Blockade Runner') by splicing a pair of these kits together (the larger scale kits becoming a wash when making a larger boat in a smaller scale).